Field of the Invention
The present invention relates to a position detecting device to detect a relative position of a magnetic detecting element with respect to a magnetic scale.
Description of the Related Art
Conventionally, there has been known a position detecting device provided with a magnetic scale and a magnetic detecting element, as a position detecting device to detect an accurate displacement position of linear displacement, rotational displacement, or the like. The position detecting device is widely utilized for an electronic component mounting device which requires a highly-accurate positioning control of a conveyed object, a detecting (measuring) device which detects (measures) a size of a component, and the like, for example.
FIG. 15 is a diagram showing an arrangement example of a magnetic scale and magnetic detecting elements of a conventional magnetic-type position detecting device. The example of FIG. 15 shows a case of detecting linear displacement and includes a magnetic scale 1 configured with a magnetic medium. In the magnetic scale 1, magnetization directions of an S-pole and an N-pole are inverted every certain distance. One repetition unit of the S-pole and the N-pole is one wavelength of a recording signal of the magnetic scale 1.
The position detecting device includes a detecting section 2 where magnetic detecting elements 3a to 3h are disposed, at a position close to the magnetic scale 1. An AMR (Anisotropic Magneto-Resistance) element utilizing an anisotropic magneto-resistance effect is used for the magnetic detecting elements 3a to 3h, for example. In the magnetic detecting device, the magnetic scale 1 is disposed on the fixed side and the detecting section 2 is disposed on the movable side, and the position detecting device is configured to detect a relative position of the detecting section 2 with respect to the magnetic scale 1.
FIG. 16 is a diagram showing an arrangement example of the eight magnetic detecting elements 3a to 3h. FIG. 16A shows an element arrangement of the magnetic scale 1 viewed from the upper face of the magnetic scale 1, and FIG. 16B is the element arrangement of the magnetic scale 1 viewed in the cross-sectional direction.
The magnetic scale 1 is magnetized to have the N-poles and the S-poles at a certain interval in the longitudinal direction. Then, a magnetic signal to be detected by the detecting section 2 has a wavelength λ corresponding to one period in which the N-pole and the S-pole change. An electric signal outputted by the detecting section 2 has a pitch P corresponding to a half of the wavelength λ. The N-poles and the S-poles are arranged linearly at an interval of one pitch.
The four magnetic detecting elements 3a to 3d are adjacently disposed close to the magnetic scale 1. For the arrangement interval of the four magnetic detecting elements 3a to 3d, as shown in FIG. 16A, the two magnetic detecting elements 3a and 3b are arranged having an interval of one pitch P, and the other two magnetic detecting elements 3c and 3d are arranged having an interval of one pitch P. Then, the magnetic detecting element 3a and the magnetic detecting element 3c are disposed at positions (n+½)P apart from each other, in which n is an integer. The four magnetic detecting elements 3a to 3d are connected in series. A series circuit connecting the four magnetic detecting elements 3a to 3d in series is connected between a point of a predetermined potential V and an earth potential portion GND, and a signal Ch+ is taken out from a middle point of the series circuit (i.e., connection point of the magnetic detecting elements 3b and 3c).
Moreover, the other four magnetic detecting elements 3e to 3h are disposed apart from the four magnetic detecting elements 3a to 3d by a certain distance (m+½)P, in which m is an integer. The four magnetic detecting elements 3e to 3h are connected in series having the same arrangement interval as the magnetic detecting elements 3a to 3d. Then, a series circuit connecting the four magnetic detecting elements 3e to 3h in series is connected between the point of the predetermined potential V and the earth potential portion GND, and a signal Ch− is taken out from a middle point of the series circuit (i.e., connection point of the magnetic detecting elements 3f and 3g).
FIG. 17 is a diagram showing a connection configuration to obtain the detection signals from the eight magnetic detecting elements 3a to 3h. 
The signal Ch+ obtained from the middle point of the four magnetic detecting elements 3a to 3d and the signal Ch− obtained from the middle point of the four magnetic detecting elements 3e to 3h are supplied to an operational amplifier 4. In the operational amplifier 4, both of the signals Ch+ and Ch− are amplified and taken out as a detection signal.
By taking out the signals detected by the magnetic detecting elements 3a to 3h using the configuration shown in the FIG. 16 and FIG. 17, it is possible to obtain the detection signal for detecting the relative position with respect to the magnetic scale. That is, pairs of the elements 3a and 3b and the elements 3c and 3d among the four magnetic detecting elements 3a to 3d are arranged having an interval corresponding to one fourth of one wavelength of the recording signal, and thereby signal changes detected in the respective pairs have opposite phases. That is, the signal Ch+ taken out from the middle point of the series circuit configured with the four magnetic detecting elements 3a to 3d and the signal Ch− taken out from the middle point of the series circuit configured with the four magnetic detecting elements 3e to 3h have phases opposite to each other.
Moreover, the signals Ch+ and Ch− are supplied to the operational amplifier 4, and the amplified detection signal is obtained from the operational amplifier 4. Here, by the amplification configuration of the operational amplifier 4 using a bridge configuration as shown in FIG. 17, the detection signal can be obtained stably from the operational amplifier 4, and it is possible to contribute to the improvement of a position detection accuracy. That is, since the variation of a resistance value in each of the elements with respect to temperature change can be canceled, the detection signal becomes strong against the temperature change applied to the elements. Further, by the use of a differential amplifier as the operational amplifier 4, the signal level becomes approximately twice, and also, since noises having the same phase can be eliminated, it is possible to obtain a preferable detection signal which is strong against external disturbance noise.
Patent literature 1 describes an example of the above magnetic-type position detecting device.